A gigantic, spinning, dead black spherical object dubbed YU55 and approximately of the same bulk as a nuclear aircraft carrier is expected to make a close pass by planet Earth on Tuesday night, coming well inside the orbit of the Moon.
NEO YU55 imaged by the Arecibo radar telescope. Credit: NASA Looks a bit like that thing from …

Earth's gravity

Because

The moon wasn't captured by earth, it formed from the stuff that was already floating around earth. Stop me if I get too technical. Most of the crap that was thrown into space when the other planet hit earth actually landed back on earth, some of it flew off into space but only a small amount had the right speed to start orbitting earth. This all formed together and made le moon. Most stuff that approaches us will either collide with us or sod off again. The speed and angle needed for earth to capture another body is quite unlikely, but possible.

If you had a bowling ball in the middle of a trampoline and you start rolling marbles towards it, it's very hard to get the marbles to do a whole orbit around the bowling ball. Obviously friction would stop it from orbitting for any significant period of time, but you get the idea about trajectory and speed from this simple experiment.

Nah

That's not a mass extinction size. From memory, the collision that did for the dinosaurs was of a rock something around 10 miles across, massively larger than the rock we're talking about here. And even that didn't immediately wipe out the dinosaurs, the final extinction was a slower process around the change in the ecosystem that the impact caused.

coooool! So slingshot?

Read a book or two?

a) Of course it is affected by the Earth's gravity, as well the gravity of the Moon, the Sun, and absolutely everything else in the universe that has mass. That includes the dense posts to this forum (electrons have mass before anyone shoots me down).

See: http://en.wikipedia.org/wiki/Newton%27s_law_of_universal_gravitation if you slept through physics at school, or went to school after the 1980's when they apparently decided science was too hard and we should all study hotel management.

b) The reason the thing doesn't crash in to your head is because it has too much momentum. If you attached a car to a tree with a really long elastic band (office type) and then drove past the tree at 100mp/h, do you think the car would keep going, the tree would fall over or something else would happen? (Answer: the car would speed up a tiny bit as the elastic band contracted, then slow down a tiny bit as the car starts stretching the band again). Not how gravity works, but a reasonable analogy nonetheless.

Eventually the combined gravitational effects of the Sun, Earth and Moon (plus anything else in the solar system the object passes reasonably near by) might alter its orbit enough that the Earth happens to be in the way when the object is passing by. That is no more the Earth 'pulling the object down' than a sniper's bullet is pulled in to your head. Rather it's case of being in the wrong place at the wrong time.

All that momentum would be transferred in to radiation(heat/light), sound, bits of rock and bits of you flying off in all directons, plus the earth's orbit and rotation would alter a small amount; vastly less than aforesaid car when a gnat splats on the windscreen.

See: http://en.wikipedia.org/wiki/Angular_momentum

c) No it wouldn't be game over. This object is far to small to have a significant effect. Depending on what it was made from and how fast it was travelling, it would most likely break up in the atmosphere and chunks would hit the ground. There would be an impressive bang and you certainly wouldn't want to be too close to the impact, as tt would leave a crater about a mile wide and a third of a mile deep.

There would be no fireball and if you were (say) 500 miles away, you probably wouldn't even wake up to notice anything had happened. You'd be watching it on the news over your toast if it hit land in an inhabited aread. Most likely it would fall in to the ocean and nobody would even notice.

If you want to play 'End of the world', see: http://impact.ese.ic.ac.uk/ImpactEffects/

That would depend on it's mass and velocity

That is one good candidate for capture

I say we grab it. Even if it is not a station now , it can become one.

Much more worthy technological goal than the "expedition to Mars" and stuff. If we manage to get it to L1 or L2 between Earth and Moon it will sit nicely there and be 100 time more useful than a moon base.